Maintaining roll temperature uniformity in fuser roll systems has long been a problem when varying media sizes. Using a heat pipe as a fuser roll is a known technique to solve such temperature uniformity issues. Problems arise though in the complexity in the design of such heat pipe fuser rolls, because heat pipes are closed systems, and applying heat internally is difficult. Applying heat at one end of the fuser roll to simplify the geometry of the subsystem is also commonly done. By applying heat at one end of the system, incident heat flux at that one end is increased. In low mass, “instant-on” or rapid warm-up fuser roll systems, the low mass of the heat conductive fuser rolls increases the heat differentiation much more rapidly and creates a greater thermal difference than in conventional fusing systems. In an instant-on system, it is generally preferable to use a heat pipe with a low volume of fluid, such as water or water-alcohol in order to more rapidly exchange heat from the high temperature areas to the colder regions of the fusing system rolls. Some heat pipe systems incorporate a fiber wicking device to sustain the fluid in the heat pipe. In this minimal fluid configuration, there is a potential for dry-out of the heat pipe evaporator. Means to pump fluids using more complex interior geometries are also well known and used to prevent evaporator dry-out.
Low energy usage requirements in a fuser roll/pressure roll system may be met by minimizing the thermal mass of the fuser roll. Temperature uniformity may be met by heating element profile and design. Usually, these systems are optimized around the media size and weight most used in the market place. However, the need still exists to handle various media widths and substrate thicknesses, which gives rise to temperature non-uniformity along the fuser roll axis. Another factor that contributes to temperature non-uniformity is conductive and convective heat losses from the heating lamps and the fuser roll, for example, to the bearings and supporting framework.
Axial temperature non-uniformity is depicted in FIG. 1, in which the temperature of the fuser roll surface is plotted against the axial position for a 200 copy run of both short-edge feed and long-edge feed 8.5″×11″ paper. FIG. 1 describes the relative temperatures along a longitudinal axis of a fuser roll in various configurations as described. Higher temperatures to the right of the graph represent low mass, “instant-on” and rapid warm-up fusing systems as they exist currently exhibiting the temperature gradient within and outside the paper path for various sized media. Other temperature profiles exhibit the effectiveness of the present invention on temperature gradients and achievement of subsequent relative temperature uniformity. In FIG. 1, the temperature of the fuser roll outside the short edge feed paper path is higher than the temperature of the fuser roll inside the paper path by about 76° C. To address this problem, usually a system of two or more heating lamps with associated sensors and controllers is used. FIG. 2 illustrates the axial power distribution, and the ability to achieve relative temperature uniformity by employing a two heat lamp system within a fuser roll in a static state without the influence of heat loss via heat conduction to the passing media substrate. FIGS. 1 and 2 show that such a system with optimized distributed heating lamp profiles may provide a desired temperature uniformity by selectively turning lamps off and on depending on the size and weight of media used.